Technical Field
The present application relates to an electronic control apparatus for driving a motor, and more particularly to an electronic control apparatus including a switching element and a drive circuit.
Description of the Related Art
Conventionally, a motor drive circuit for driving a motor is known. For example, JP-A-2007-288856 discloses a motor drive unit described below as a conventional electronic control apparatus including a switching element and a drive circuit.
The motor drive unit includes a power transistor and a gate driver. The gate driver includes first and second current sources, a gate current controller, and a gate switching controller. The first current source is connected between a positive terminal of a circuit power supply and a gate of the power transistor. The second current source is connected between the gate of the power transistor and a negative terminal of the current power supply. The gate current controller is connected to the first and second current sources. The gate switching controller is connected to the gate current controller.
The gate current controller drives a first power transistor by controlling the first and second current sources based on signals inputted from the gate switching controller. When the signal inputted from the gate switching controller gives an instruction to turn ON the power transistor, the gate current controller controls the first current source and supplies a predetermined current to the gate of the first power transistor. As a result, the gate voltage becomes higher than an ON/OFF threshold voltage, and the power transistor is turned ON.
On the other hand, when the signal inputted from the gate switching controller gives an instruction to turn OFF the power transistor, the gate current controller controls the second current source and withdraws a predetermined sink-current from the gate of the power transistor. As a result, the gate voltage becomes lower than the ON/OFF threshold voltage, and the power transistor is turned OFF.
When an abnormality occurs in the first current source in the above-described motor drive unit, the gate voltage of the power transistor does not decrease. An abnormal state may occur in which the power transistor cannot be turned OFF. At this time, when the gate voltage of the power transistor is a voltage within a predetermined range near the ON/OFF threshold voltage, the drain-source voltage, or in other words, the ON voltage increases, and heat generation by the power transistor increases. When an abnormal state such as this continues, the power transistor may generate heat and thermal damage may occur.